21506265541 has 4 divisors (see below), whose sum is σ = 21506814432. Its totient is φ = 21505716652.

The previous prime is 21506265533. The next prime is 21506265551. The reversal of 21506265541 is 14556260512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21506265541 - 2³ = 21506265533 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21506265541.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506265551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 210745 + ... + 295678.

It is an arithmetic number, because the mean of its divisors is an integer number (5376703608).

Almost surely, 2^21506265541 is an apocalyptic number.

It is an amenable number.

21506265541 is a deficient number, since it is larger than the sum of its proper divisors (548891).

21506265541 is an equidigital number, since it uses as much as digits as its factorization.

21506265541 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 548890.

The product of its (nonzero) digits is 72000, while the sum is 37.

The spelling of 21506265541 in words is "twenty-one billion, five hundred six million, two hundred sixty-five thousand, five hundred forty-one".